Electromagnetic hysteresis unit

ABSTRACT

The invention is based on an electromagnetic hysteresis unit ( 1, 23 ) with magnetic north pole ( 4 ) which are arranged to alternate with magnetic south pole ( 5 ) on a magnet body ( 2, 3 ) in a peripheral direction ( 15 ) about an axis of rotation ( 14 ) at a distance from the magnetic south poles ( 5 ). The magnet body ( 2, 3 ) comprises a magnet coil ( 6 ). A hysteresis ring ( 16 ) connected with a rotor ( 17 ) can be moved with a slight play in relation to the poles ( 4, 5 ). It is proposed that the peripheral surfaces of the north pole ( 4 ) and south pole ( 5 ) lie on the same circle and opposite the same peripheral surface of the hysteresis ring ( 16 ). Thereby is created a radial construction space for embedding the hysteresis ring ( 16 ) in the rotor ( 17 ) which consists of material of good heat conductivity and optionally for providing cooling ribs.

FIELD OF THE INVENTION

The invention relates to an electromagnetic hysteresis unit.

BACKGROUND OF THE INVENTION

By electromagnetic hysteresis units will be understood hereinafter ashysteresis brakes and hysteresis clutches. The method of operation ofthe hysteresis units is based on a magnetic action force of poles thatattract each other in the synchronous running and on a constant magneticreversal of a magnetically, semi-hard material, namely, of a hysteresisring in the slip operation.

Unlike eddy-current clutches and brakes in hysteresis units, which arebased on a different physical principle, the transmissible torque is, toa great extent, independent of the slip rotational speed.

The best known design of such hysteresis units consists of a magnet bodywith one exciting coil each having an outer and inner pole ring withaxially aligned superposed soft iron poles in the same number andspacing, wherein the outer poles are disposed offset in peripheraldirection relative to the inner poles in the stationary state or duringsynchronous running by half a spacing and have an opposite polarization.In the radial intermediate space of the pole rings, the hysteresis ringcan rotate as a thin-walled, bell-shaped part without contact.

When magnet coils are traversed by current, a substantially radiallyoriented magnetic field generates between the poles of oppositepolarity. But the pole off-set produces an alternatively tangentialreorientation of the magnetic flow in the hysteresis ring and thus apermanent reverse magnetization of all elementary magnets when thehysteresis ring rotates relative to the magnetic body. Therefrom resultsa torque which depends only on the exciter flow. It can be regulated andcontrolled by adequately changing the exciting current. Such hysteresisunits are known as clutch, e.g. from U.S. Pat. No. 2,488,827. Here thehysteresis ring is disposed radially between two parts of a rotatablemagnet body which parts are connected by a disc of non-magnetizablematerial.

From DE 197 05 290 A1 is further known a hysteresis brake in which ahysteresis ring surrounds a closed magnetic ring of permanent magneticmaterial whose surface facing the hysteresis ring is provided with aplurality of poles embedded on the periphery and having alternativelyopposite polarity. The magnetic ring is segmentally radially magnetizedthrough and connected with a soft iron magnet body. The hysteresis ringrotates in an annular air gap between the magnet ring and an adjustingring with slight radial play relative to the magnetic ring. Thetransmissible torque can be adjusted by an axial displacement of theadjusting ring.

The hysteresis ring is, in general, made of a material having small wallthickness and connected with a rotating part. Opposite to this, theparts provided with a large mass, such as magnet coils, magnet body,etc., are connected with the housing. In the case of a hysteresisclutch, one part of the magnet body is formed by a rotor and amagnetic-flux guiding disc connected therewith which rotates with slightplay relative to the magnet body.

Because of the air gap between the hysteresis ring and the pole rings,the torque is contactlessly transmitted. Brakes produce both a braketorque in slip operation and a retaining torque in stationary state sothat the decelerated part can also be kept in a decelerated position.Hysteresis clutches transmit torques both in synchronous running duringwhich the coupled parts have the same rotational speed and in slipoperation during which the parts to be coupled still have rotationalspeed difference. The transmissible torques depend only on the currentin the exciting coil and can be continuously adjusted up to anadmissible maximum value based on the type.

The power loss resulting in the slip operation heats the thin-walledhysteresis ring very quickly. The heat can be removed only verydeficiently, via the small material thickness of the hysteresis ring, tothe adjoining parts in order to be eliminated therefrom by further heatconduction and convection. The admissible permanent slip power on oneside and the briefly removable slip work on the other are thus verylimited.

Such hysteresis units are used, among others, for traction regulationfor the processing of drawn endless products like wire, cable, rope,sheets, paper, threads, etc. They are also used for brake torqueregulating systems and for a load simulation such as for test stands,ergometers, etc.

The problem on which the invention is based is to improve in the slipoperation the brief and also the permanent thermal load of a hysteresisunit.

SUMMARY OF THE INVENTION

According to the invention the peripheral surfaces of the north polesand south poles lie on the same circle, the center of which lies on theaxis of rotation. They also lie opposite the same peripheral surface ofthe hysteresis ring. Thereby the hysteresis ring is able to rotate onone peripheral surface at short distance from the magnets while on theother peripheral surface it is embedded in a rotor made of materialhaving good heat conductivity which can also have cooling devices suchas in the form of cooling ribs. It is thus ensured that the heataccumulated be thoroughly removed and that great slip torques can betransmitted for a long time.

The hysteresis ring conveniently surrounds the north poles and the southpoles so that it lies with the adjoining rotor parts on the outerperiphery of the hysteresis unit. Thereby result, on one hand, largeheat radiation surfaces and, on the other, the rotor generates in thisarea itself a great air movement which favors the convention. In theperipheral area of the rotor cooling ribs are conveniently disposedwhich can be aligned both axially and in peripheral direction and can beinterrupted by slots.

In one development of the invention, the poles are formed by polefingers which, departing from axial front walls of the magnet body, arefitted upon each other and have between them a larger distance than fromthe hysteresis ring so that the magnetic flux leads from a north pole toa south pole via the hysteresis ring. The pole fingers can hereadvantageously overlap in peripheral direction.

The pole fingers, which extend substantially axially, taper toward theirfree end in axial direction and/or in peripheral direction. Therebymaterial and weight are spared and a good magnetic flux obtained. Inparticular, the tapering in peripheral direction produces a very uniformdistribution of the magnetic flux between adjacent pole fingers so thatthe hysteresis ring uniformly absorbs energy on its breadth and localtemperature peaks are prevented.

The magnet body can be easily produced with its pole fingers when it isdivided in a radial plane, each separate part of the magnet bodyreceiving the pole finger of one polarity. A centering ring reciprocallycenters the two parts of the magnet body which are usuallyinterconnected with screws,.

To keep the rotating masses small, it is advantageous that the magnetbody with the magnet coil be disposed fastened on the housing and to usea free space between the pole fingers for current supply. In combinationwith a pot-shaped rotor open on one side, current can be suppliedwithout an expensive sliding ring arrangement subject to wear.

To increase the stability of the pole fingers, the same as to preventvibrations and flow noises, it is convenient that the pole fingers beinterconnected by a non-magnetizable material. If the material,preferably brass, has good heat conductivity, it can, at the same time,serve uniformly to distribute the accumulated heat and remove it to theoutside. The material can be advantageously introduced as fillingcomposition in the intermediate spaces between the pole fingers or beformed by a connecting ring upon which the pole fingers are shrunk.

When the hysteresis unit is designed as clutch, an outer part of thefirst magnet body is conveniently separated by an annular gap andconnected with the second magnetic body via the non-magnetizablematerial. The rest of the first magnet body with the coil are mountedfastened on the housing while the second magnet body sits on a part tobe coupled and is rotatably supported with a small gap relative to thefirst magnet body. A second part to be coupled is non-rotatablyconnected with the hysteresis unit which carries the hysteresis ring.

BRIEF DESCRIPTION OF THE DRAWING(S)

Other advantages result from the description of the drawing thatfollows. An embodiment of the invention is shown in the drawing. Theexpert will conveniently regard the features also separately and makewith them logical added combinations. In the drawing:

FIG. 1 is a longitudinal section through a hysteresis brake;

FIG. 2 is a section corresponding to the line II—II in FIG. 1;

FIG. 3 is a partial development of a hysteresis ring and a few polefingers according to FIG. 1;

FIG. 4 is a longitudinal section through a hysteresis clutch wherein theupper half shows a design with connecting ring and the lower half adesign with a filling compound;

FIG. 5 is a partial development of a hysteresis ring and a few polefingers according to FIG. 4, upper half; and

FIG. 6 is a partial development of a hysteresis ring and a few polefingers according to FIG. 4, lower half.

DETAILED DESCRIPTION OF THE INVENTION

The hysteresis unit shown is a hysteresis brake 1. It has a dividedmagnet body 2, 3 which comprises one magnet coil 6. The magnet body isdivided in a radial plane. The two parts 2 and 3 thereof are centeredrelative each other by a centering ring 8 and interconnected by screws9. The magnet body 2, 3 consists of soft iron and has on its outerperiphery pole fingers 4, 5 which extend substantially axially and arealternatively integrated on the part 2 or part 3 of the magnet body.

If the magnet coil 6 is supplied with current, via a current supply 7,the pole finger 4 form, in the embodiment shown, a north pole on part 2of the magnet body while the pole finger 5 form south poles on part 3 ofthe magnet body. The magnet body 2, 3 is mounted fastened to thehousing. Thereby the current supply 7 can be easily shifted through oneof the free spaces 19 formed between the pole fingers 4, 5.

In the magnet body 2, 3 is supported, by ball bearings 10, 11, a shaft12 which rotates around an axis of rotation 14. The shaft 12 carries onits ends fitting keys 13 by which rotating parts (not shown in detail)can transmit a torque to the shaft 12. On the shaft 12 sits firmly on apot-shaped rotor 17 open on one side in which is embedded a hysteresisring 16 made of magnetically semi-hard material. The shaft 12 is axiallyfixed between a collar 22 on the rotor 17 and a guard ring 21 embeddedin the shaft 12. The rotor 17 itself is made of material having goodheat conductivity and can support cooling devices in the form of coolingwebs 18 in order to improve the heat conduction and convection. Thecooling webs 18 can extend in peripheral direction or axially and havenotches and/or bores.

FIG. 2 shows that the distance between the pole fingers 4, 5 is greaterthan the distance between the pole fingers 4,5 and the hysteresis ring16. Thereby the hysteresis ring 16 is flowed through according to themagnetic flux 20. During a relative movement of the hysteresis ring 16in peripheral direction 15 toward the magnet body 2, 3, the polarizationof the elementary magnetic zones produced in the hysteresis ring 16 isreverse whereby a considerable torque can be transmitted. The torqueprimarily depends on the intensity of the current flowing through themagnet coil 6. As a result of the power loss in the slip operation whichresults from the reversal of polarization of the hysteresis ring 16, agreat amount of heat accumulates in it. The amount of heat is, ofcourse, removed via the rotor 17 and given off to the environment sothat in comparison to known hysteresis units great torques can betransmitted in the slip operation without an overheating of thehysteresis brake having to be feared.

According to FIG. 4, the hysteresis unit 23 is a clutch. It differs fromthe hysteresis unit 1 of FIG. 1 designed as a brake by the fact that thefirst magnet body 2, which is mounted fastened on the housing, has anouter part 25 which is separated by a narrow annular gap 26 from theother first magnet body 2. The outer part 25 is connected via aconnecting ring 27 made of non-magnetizable material, preferably brass,with the second magnet body 3 by it being shrunk by its pole finger 4and the second magnet body 3 by its pole finger 5 upon the connectingring 27 (upper halves of FIG. 4 and FIG. 5). The connecting ring 27,which can also be used in a hysteresis unit 1 according to FIG. 1,imparts to the hysteresis unit 23 a great stability and serves at thesame time for better distribution and removal of heat.

The second magnet body 3 sits upon a part to be coupled and is rotatablysupported relative to the first magnet body 2 from which it is separatedby an annular gap 26 and by a gap 29. The other part to be coupled isnon-rotatably connected with rotor 17 in which the hysteresis ring 16 isembedded. The rotor 17 has on the outer periphery grooves 24 to enlargethe surface and thereby better to remove the heat. At the same time, theperiphery of rotor 17 can be designed as belt pulley for a drivemechanism.

In the variant according to the lower half of FIG. 4 and according toFIG. 6, the intermediate spaces between the pole fingers 4, 5 are filledwith a non-magnetizable filling compound 28 which creates the connectionbetween the outer part 25 of the first magnet body 2 and the secondmagnet body 3. The filling compound 28 is conveniently introduced in theintermediate spaces by a casting or sealing technique. As fillingcompound can be used, for example, a non-magnetizable metal like brassor also a plastic material.

Reference Numerals

1 hysteresis unit

2 first magnet body

3 second magnet body

4 pole finger, north pole

5 pole finger, south pole

6 magnet coil

7 current supply

8 centering ring

9 screw

10 ball bearing

11 ball bearing

12 shaft

13 fitting key

14 axis of rotation

15 peripheral direction

16 hysteresis ring

17 rotor

18 cooling webs

19 free space

20 magnetic flux

21 guard ring

22 collar

23 hysteresis

24 grove

25 outer part

26 annular gap

27 connecting ring

28 filling compound

29 gap

We claim:
 1. A hysteresis unit (1, 23) comprising a magnetic north pole(4) around an axis of rotation (14), alternating at a distance in aperipheral direction (15) from a south pole (5) situated in a magnetbody (2, 3) having a magnet coil (6), a movable hysteresis ring (16)having a slight play relative to said poles (4, 5) is connected with arotor (17), and peripheral surfaces of the north pole (4) and south pole(5) lie on the same circle and opposite to an adjacent peripheralsurface of said hysteresis ring (16), the moveable hysteresis ring (10)surrounds said north pole (4) and said south pole (6), said poles beingformed by pole fingers (4, 5) which, departing from axial front walls ofsaid magnet body (2, 3) are aligned upon each other and are spaced fromeach other a greater distance than from said hysteresis ring (16) andsaid hysteresis ring (16) abuts by a peripheral surface on said rotor(17), and wherein said pole fingers (4, 5) are interconnected by anon-magnetizable material.
 2. The hysteresis unit (1, 23) according toclaim 1, wherein said non-magnetizable material is preferably brass,which has good heat conductivity.
 3. The hysteresis unit (1, 23)according to claim 1, wherein said pole fingers (4, 5) are supported byand shrunk upon a connecting ring (27).
 4. The hysteresis unit (1)according to claim 1, wherein intermediate spaces between said polefingers (4, 5) are filled with a non-magnetizable filling component(28).
 5. The hysteresis unit (1, 23) according to claim 1, wherein it Isdesigned as a clutch by an outer part (25) with said pole finger (5) ofsaid magnet body (2) being separated from the latter by a thin annulargap (26) and said second magnet body (3) sitting with a small gap (29)rotatably relative to said magnet body (2) upon a rotatable part to becoupled while the first magnet body (2) is mounted fastened on ahousing.
 6. An electromagnetic hysteresis unit (1, 23) comprising: amagnet body (2, 3) having a magnet coil and multiple magnetic northpoles (4) arranged alternatively (15) with multiple magnetic south poles(5) spaced an a tangential distance from each other around an axis ofrotation (14) with peripheral surfaces of the north poles (4) and southpoles (5) lie on the same circle; a movable hysteresis ring (16) havingslight play relative to said magnetic north and south poles (4, 5) andis connected to a rotor (17), said hysteresis ring (16) surrounds saidnorth poles (4) and said south poles (5), said poles are formed by polefingers (4, 6) which extend from axial facing surfaces of said magnetbody (2, 3) and are directed towards each other having a greaterdistance from each other than from said hysteresis ring (16) and saidhysteresis ring (16) abuts a peripheral surface on said rotor (17); andwherein said rotor (17) consists of a material having good heatconductivity in order to improve the heat conduction, that said magnetbody (2, 3) is constructed in two parts and divided in the area of themagnet coil (6) that said rotor (17) is firmly mounted on a shaft (12)that is supported in said magnet body (2, 3) by means of two ballbearings (10, 11), a collar (22) of said rotor (17) and a guard ring(21) mounted on said shaft (12) forming axial stops on which abuts arespective inner ring of one of said ball bearings (10, 11) while outerrings of said ball bearings abut on axial stops each formed by one ofsaid two parts of said magnet body (2, 3) and that said magnet body isthick walled, the pole fingers being integral in the two parts of saidmagnet body and being tapered to their free end in axial directionrelative to their radial and tangential extension and being tapered to apoint relative to their radial expansion.
 7. The hysteresis unit (1, 23)according to claim 6, wherein said rotor (17) has cooling devices (18).8. The hysteresis unit (1, 23) according to claim 6, wherein said polefingers (4, 5) overlap in peripheral direction (15).
 9. The hysteresisunit (1, 23) according to claim 6, wherein said magnet body (2) Isfastened to a housing and the current supply for supplying electriccurrent to the magnetic coil (7) is shifted through a free space (19)formed between said pole fingers (4, 5), said rotor being pot-shaped anddefining an opening on one side.
 10. An electromagnetic hysteresis unit(1, 23) comprising: a magnet body (2, 3) constructed by a first part anda second part having a magnet coil (6) positioned between the first andsecond parts to induce a north pole in the first part and a south polein the second part; a plurality of first pole fingers having theelectromagnetically induced north pole extending from a first axial faceof the first part of the magnet body being electromagneticallycircumferentially arranged with a plurality of second pole fingershaving the electromagnetically induced south pole extending from asecond axial face of the second part of the magnet body; a shaftsupporting the first and second parts of the magnet body (2,3) via arespective first and second bearings enabling relative rotationalmovement between the shaft and the magnet body; a rotor (17) fixed tothe shaft substantially surrounds the first and second parts of themagnet body, the rotor (17) having an inner peripheral face supporting amovable hysteresis ring (16) having a slight spacing relative to anouter peripheral face of the magnet body defined by the alternatelycircumferentially arranged first and second pole fingers of said firstand second parts of the magnet body; the alternately circumferentiallyarranged first and second pole fingers (4, 5) which extend fromrespective axial faces of said magnet body (2, 3) are aligned at anequal radial distance from the hysteresis ring and are interlacedtowards each other and spaced from a respective adjacent pole finger agreater distance than the slight spacing from said hysteresis ring (16);and wherein the magnet body (2, 3) is radially divided by the magnetcoil (6) and both the first and second parts being centered relative toeach other and interconnected via a centering ring (8). collar (22)portion of said rotor (17) abuts with an inner ring of the first bearing(10) to form a first axial stop, and a guard ring (21) mounted on saidshaft (12) abuts an inner ring of the second bearing (11) while outerrings of said first and second bearings abut on axial stops each formedby said respective first and second parts of the magnet body (2, 3). 11.The electromagnetic hysteresis unit (1, 23) as set forth in claim 10wherein the first and second pole fingers are integrally connected by abase portion to the respective first and second pass of said magnet bodyand axially and radially taper to a free end edge which is narrower thanthe base portion.
 12. The electromagnetic hysteresis unit (1, 23) as setforth in claim 10 wherein the first and second parts of the magnet body(2, 3) are secured together by an axially aligned bolt spaced a radialdistance from the axis and extending through the first and second partsof the magnet body.